Device for measurement of high temperature



Dec. 31, 1963 D. s. SCHWARTZ DEVICE FOR MEASUREMENT OF HIGH TEMPERATURE Filed Aug. 50, 1961 5 Sheets-Sheet 1 E3 INVENTOR.

CAP. ORO/54. CoA/6T Dec.. 3l, 1963 D. S. SCHWARTZ DEVICE FOR MEASUREMENT OF HIGH TEMPERATURE Filed Aug. so, 1961 3 Sheets-Sheet 2 ME45. HEI/ICE i ME4S. .PEV/CE INVENTOR.

Dec. 31, 1963 D. s. SCHWARTZ 3,115,779'

DEVICE FOR MEASUREMENT OF HGH TEMPERATURE Filed Aug. 30, 1961 3 Sheets-Sheet 5 jam?. 20

United States Patent O Filed Aug. 30, 195i, Ser. No. l35,027 Claims. (Cl. '7S- 362) This application is a continuation-in-part of application Serial No. 762,881, entitled Device of Measurement of High Temperature, filed September 23, 1958, now abandoned.

This invention relates to an apparatus for the measurement of high temperatures and in particular to such an apparatus useful in environments wherein the apparatus is to be located at a point remote from the temperature indicating point.

Several techniques have been, heretofore, used in the measurement of high temperatures. These include the use of optical and radiation pyrometers, thermocouples and resistance thermometers, interferometers and pyrometric cones. All of these possess inherent disadvantages or limitations for measuring very high temperatures or temperatures in induction furnaces. For example, in optical pyrometers, stable clear optical paths are necessary which may not be readily obtainable due to the location of the high temperature environment involved. Thermocouples and resistance thermometers are not practical for temperatures above i800" to 2C0O F, and in induction furnaces Where the problem of current induction produces undesired heating and spurious signals. lnterierometers have numerous limitations including the dilliculty in utilizing the same in induction furnaces. Pyrometric cones are useful only in providing single static temperature indications, so they cannot be used for continuous readings of varying temperatures.

Accordingly, it is an object of the present invention to provide high temperature measuring apparatus which do not have the disadvantages and limitations referred to above. More particularly, it is an object of the present invention to provide high temperature measuring apparatus which provides a temperature variable electrical characteristic which can be readily detected and measured at a point remote from the high temperature environment involved and, further, where the apparatus is useful at temperatures greatly in excess of the temperatures at which thermocouples and resistance thermometers have, heretofore, been used.

Another object of the present invention is to provide high temperature measuring apparatus as just described which can oe utilized in induction furnaces. Still anotherobject of the present invention is to provide apparatus as just described which can be readily utilized in extremely high temperature environments, and which is of relatively simple and rugged construction and can be used repeatedly for prolonged periods ot' time at such high temperatures.

Still another object of the present invention is to provide temperature measuring apparatus as described which can be mounted either completely within the high temperature environment involved or, in another' form thereof, can be mounted within an opening in the wall of a container or housing for the high temperature environment involved.

The above and other advantages and objects of the invention will become apparent upon making reference to the specification to follow, the claims and the drawings wherein:

FIG. l is an elevational View of a spherical embodiment of the present invention;

FIG. 2 is a sectional view through FG. l, taken sub- 3,ll5,779 Patented Dec. 3l, 1963 stantially along the line 2 2 therein and further including, in diagrammatic form, various elements which are connected to the apparatus shown in FIG. l;

Fl'GS. 3 and 3A are views of a modified spherical form of the present invention constituting an improvement upon the embodiment shown in FlG. 2;

FIG. 4 is a graph showing the variation of dielectric constant (or capacitance) with temperature of a piezocapacitive temperature responsive element forming a part of the apparatus shown in FIG. 3;

FIG. 5 is a sectional view through a cylindrical embodiment of the present invention;

FIGS. 6 and 6A are views of a modified form of the spherical embodiment of the invention shown in FIG. 3;

FlG. 7 shows curves illustrating the variation in temperature with thickness of the spherical high temperature measuring apparatus shown in FlG. 6; and

FIG. 8 is a sectional View through a still further modilied form of the invention inserted in the opening in a wall surounding the high temperature environment to be measured.

Refer now to FIGS. l and 2 which illustrate a simple form of the present invention. A spherical temperature sensing unit 8 is shown which is inserted directly into the high temperature environment to be measured. Although the spherical shape illustrated is preferred, other shapes could be utilized. The unit comprises a spherical hollow body or shell itl most advantageously having relatively thick Walls made of a high temperature refractory, such as alumina, mullite, or the like. These materials are relatively poor conductors of heat and electricity over the range of temperatures to be measured. For example, mullite has extremely high heat and electrical qualities for temperatures Well in excess of 5000 F.

The shell il@ has a spherical cavity l2 therein. A pair of spaced bores ld-li extend through the walls of the shell lh. A pair of cylindrical bushings .l5-l5 preferably made of the same material as the shell liti project from the outer surface of the shell lll and the bushings have bores idf-ld forming extensions of the shell bores l/l`lid. The bushing could be made integral with the shell, but are shown as originally separate elements aixed to the shell lo by a suitable cement which may be Sauereisen or other high temperature cement. The spherical shell l@ may be initially made from two hemispherical body halves which are cemented together by a suitable refractory cement.

Pipes l and i8 are shown extending into the cavity l2 of the shell lll through the bores .idld and lill-i4. The bushings id l' serve to insulate the pipes i7 and litt from the surrounding high temperature and, when the temperature sensing unit lil is mounted in a temperature environment the ends of the bushings extend against a wall Ztl surrounding the high temperature environment involved. The pipes i7 and l extending through the aforesaid bores and wall Ztl respectively carry a coolant into and out of the cavity l2 so that the defining walls of the cavity are at a temperature much lower than the temperature on the outside of the shell lil. The magnitude of the temperature gradient is increased by using thicker walls for the shell It@ and a material having greater heat insulating qualities. Where the temperature to be measured is expected to vary over short time intervals, the shell wall thickness can be such as to provide too long a time constant to enable the cavity temperature to catch up with the variation in the outside temperature. ln such case, a thinner wall thickness and/or a higher heat conductivity material is used. However, the cooling problems become more severe in the latter case. lt is readily possible for high temperature environments of a the order of 5000" F. to reduce the temperature on the inside of the shell to the order of 100 C A temperature responsive element 22 is positioned within the cavity l2 to measure the temperature thereof. From data on the thickness of the shell walls, the temperature indicated by the temperature responsive element 22, the rate of llow and the temperature differential of the incoming and outgoing coolant, the temperature on the outside of the shell l@ can be calculated from well known heat flow equations. However, it is more convenient to determine the outside temperature by calibration procedures to be explained later on in the specification.

The temperature responsive element 22 shown in FIG. 2 is a thermocouple having a pair of leads 22a and 22]) respectively extending through the bores lid-1d and FAV-2id on the outside of the pipes i7 and 13. The leads 22a and 2lb extend to any suitable temperature indicating device 23 which responds to the voltage output of the thermocouple. The device 23 may be calibrated in temperature units to indicate the temperature of the cavity l2 directly. The temperature and rate of flow of the incoming coolant flowing in the inlet pipe 17 is selectcd to provide a temperature within the cavity l2 in a range at which the thermocouple or other temperature responsive element 22 is operative. The temperature on the outside of the shell l@ can thus be far in excess of the temperature at which the thermocouple or other temperature responsive element is operative.

The inlet pipe T7 extends to the output of a pump 24 having an adjustable control knob 2.6 for controlling the rate of flow of uid in the pipes la7-liti. A ow meter 2S is provided for indicating the rate of ow of the coolant. The temperature of the incoming coolant is fixed at a given temperature by any suitable temperature stabilizing means 3@ well known in the art.

Utilizing the equipment shown in FIG. 2, two possible calibration procedures can be followed. ln one of these procedures, the temperature sensing unit S is subjected to a number of different predetermined calibration temperatures distributed throughout the range of temperatures at which the unit is to be utilized to measure unknown temperatures. At each calibration temperature, the inlet coolant temperature and the coolant flow rate is adjusted to a fixed value and the temperature in the cavity l2 for each calibration temperature measured by the temperature indicating device 23 is noted. A calibration curve can then be drawn where one of the scales of the curve represents the calibration temperature on the outside of the shell lli? and the other scale represents the temperature in the cavity l2. When the unit 8 is later placed in an unknown temperature environment, a point on the calibration curve is located corresponding to the temperature of the cavity i2 and the curve then gives the outside ten.- perature provided the inlet coolant temperature and coolant flow rate are adjusted to the values used during the calibration procedure.

Another method of Calibrating the apparatus shown in FIG. 2 is to adjust the flow rate of the xed temperature inlet coolant to a value which maintains a constant cavity temperature at the various calibration temperatures and to draw a curve from the outside temperature and flow rate values involved. This calibration curve will then give the value of an unknown outside temperature from the flow rate required to maintain the lxed calibration temperature in the cavity l2.

As previously indicated, the use of thermocouples and other similar heat sensitive elements is unsatisfactory for induction furnaces where the magnetic fields involved induce eddy currents in the metal portions of the thermocouple which cause significant excessive heating or otherwise disturb the output of the heat sensitive elements. To provide a temperature sensing unit 8 useful in a variety of environments including induction furnaces, other forms of the invention now to be described are utilized. One

such form is illustrated in FIGS. 3 and 3A. This form of the invention is identical to that shown in FIG. 2 except that the thermocouple 22 is replaced by a thin lining 22 of an insulation or semi-conductor material which otfers a high resistance to eddy currents and which provides an electrical output which varies with temperature and is substantially non-responsive to pressure variation. Tae lining 22 is made very thin relative to the thickness of the walls of the shell l@ so that only an insignificant temperature gradient exists across the lining 22.

Another advantage of using a lining of temperature responsive material rather than a thermocouple or the like is that the temperature responsive element is distributed tnroughout the shell cavity l2 and thus produces a respouse which is dependent on the average temperature within the cavity. lt is possible for hot spots to develop within the cavity so that substantial errors could be introduced if, for example, the thermocouple were located at such a hotspot.

Ferroelectric materials are especially useful as the lining material, especially non-polarized barium titanate and lead-zirconate titanate materials which have excellent ternperature responsive capacitive qualities. It is, however, important to hold the temperature of these materials below their Curie point temperatures. (Barium titanate has a Curie point of approximately C. and lead-Zirconate titanate has a lCurie point of about 325 C.) If the Curie point temperatures of these materials is exceeded, an ambiguity in the temperature indication of the capacitance characteristics of the titanate material will be present. This is illustrated by the curve Cl in FIG. 4 wherein the ordinate scale represents the dielectric constant (or capacitance) of the titanate material and the abscissa represents temperature. It will be noted that as the temperature is increased from zero, the dielectric constant or capacitance of the material reaches a peak where further increase in temperature results in a decrease in dielectric constant (or capacitance). The peak of the curve occurs at the Curie point temperature and will obviously provide ambiguity in the temperature indicated by a given capacitance measurement unless one knows on what side of the peak of the curve the temperature involved is located. Therefore, the temperature for the coolant in the inlet pipe l? (and/ or the rate of coolant iiow) is selected which will assure a temperature of the temperature responsive capacitive lining 22' below the Curie point temperature. Preferably, the temperature is selected so that the maximum expected temperature to be measured is near the Curie point temperature where the capacitance sensitivity of the titanate material is greatest as indicated by the steepness in the slope of the curve C1 in the segment of the curve immediately below the peak thereof.

The lining 22 is provided with thin metal electrodes 32 and 3d on the inner and outer surfaces thereof which represent the plates of the capacitor whose dielectric is the body of the titanate material involved. The lining 22 in the form of the invention shown in FIGS. 3 and 313i may be applied to the shell il@ by cementing flexible, thin sheet metal coated titanate material to the cavity walls of the two halves of the shell l@ before they are cemented together or by spraying the conductive and titanate layers thereon. Electrical interconnections (not shown) between the hemispherical halves of the electrodes 32 and 3d of the lining can be made before assembling the halves of the casing fr@ by wires soldered between the corresponding electrode layers forming the electrodes.

Conductors 36 and 3S respectively extend from the lining electrodes through the respective casing bores 14-14 and idf-Td to a capacitance measuring device 23. The capacitance measuring device 23 serves the same purpose as the thermocouple 2.2 in the form of the invention shown in Fl-G. 2, and the capacitance measuring apparatus may be calibrated in the manner previously described. The

thinness of the electrodes 32 and 34 and conductors 36 and 33 is such that eddy current problems present in induction furnace applications are negligible.

The movement of the coolant through the shell cavity 12 over prolonged periods can wear away the temperature responsive lining 22. To maximize the life of the apparatus, the temperature responsive capacitive lining 22 can be protected by an inner lining 39 of heat and electrical insulating material which may be made out of the same material out of which the outer shell is made.

The spherical shape of the temperature sensing unit S is distinctly preferred because of the symmetrical shape thereof which makes the positioning of the unit less critical than when non-symmetrical shapes are used. However, the elongated cylindrical shapes shown in FIGURE 5 is satisfactory for most purposes. The elements in this cylindrical form of the invention which correspond to the elements of the spherical form shown in FIG. 3 have been similarly numbered so that a description of the operation of the embodiment of FIG. 5 is unnecessary.

In all of the forms of the invention described up to this point, it is necessary to iix the inlet coolant temperature and in some cases measure the rate of tiow of the coolant. Reference should now be made to a still further improved form of temperature sensing unit 8 shown in FIGS. 6 and 6A wherein it is not necessary to fix the inlet coolant temperature or measure the flow rate of the coolant although, as above indicated, it is still necessary to maintain the lining 22 below the Curie point temperature. In this form of the invention two direct temperature measurements are obtained at different levels of thickness of a shell assembly including the aforesaid outer shell l0 and an inner shell Iii made of the identical material as outer shell I0. Except where rapid response to temperature changes is necessary, the inner and outer shells are relatively thick to establish a large temperature gradient with a modest coolant tlow rate. The :aforesaid lining 22 is sandwiched between the inner and outer shells I0 and itil', and there is further provided a temperature responsive-capacitive lining 22 on the inside surface of the shell I0 which lining may be made of the same titanate material as the outer lining 22. A protective coating or lining 39 of insulating material covers the inner surface of the lining 22 to protect the same from the coolant.

The temperature responsive inner lining 22 has inner and outer conductive coatings 32 and 3ft to which conductors 36 and 33 are connected. The latter conductors extend on opposite sides of the outlet pipe liti extending through the right hand bores I4 and 1li in the un1t 8'. with the outer lining 22 extend on opposite sides of the inlet pipe I7 passing through the bores lid and I4 of the unit 8.

As previously indicated, the conductors 36 and 38 of the outer lining 22 extend to a capacitance measuring device 23. rl`he conductors 3e" and 3S associated with the inner lining 22 extend to a capacitive measuring device 23" similar to the device 23. The capacitance measuring devices are calibrated in temperature units by subjecting the unit 8 to various calibration temperatures without cooling the unit and waiting until the entire unit 8' has reached the calibration temperature. The reading on the measuring devices 23 and 23 represent the cahbration temperature involved. t

The provision of two temperature responsive linings 22 and 22 establishes two known temperatures at different points in the shell body made up of the shells I0 and I0. Since the thickness of the inner and outer shells I0 and l0 are known, and the thickness of the linings 22 and 22 are negligible, a curve can be drawn of the temperature distribution at two points in the shell body as shown in the graph of FIG. 7, where T1 is the temperature of the inner lining 22" and point T2 is the temperaturenof the outer lining 22. By drawing a straight line LI through these two points and extending the line to The corresponding conductors 36 and 38 associated y the ordinate scale at the zero thickness point representing the outer surface of the outer shell 10, the temperature Tel on the outside of the shell body is determined since the temperature distribution is a linear function. A second line L2, is shown in FIG. 8 representing a diilerent outside temperature condition Te2. It is apparent from the slopes of lines Ll and L2 and the fact that the temperatures T2 are below the Curie temperatures (375 C. for lead-zirconate titanate and C. for barium titanate) that temperatures Tell and Te2 are not temperatures of the order of magnitude of 5000 F. If such were the case, the lines LI and L2 would be so steep that the line could not be extended to the ordinate with graph paper of reasonable size. In such case, the point at which the lines contact the ordinate can be mathematically calculated in accordance with the following formula: where ti and t?, are the thickness points of the inner and outer linings 22 and 22', TI and T2 are the temperatures of these points, and Te is the outside temperature.

It is also possible to draw a calibration curve to determine the outside temperature of the temperature sensing unit 8 by fixing the temperature of the inside lining 22 and measuring the temperature of the outer capacitive lining 2 for each calibration temperature. To this end, the inlet pipe I7 extends to the pump 24 having an adjustable iiow rate control knob 26. For each calibration temperature, the knob 26 is adjusted to x the temperature of the inner lining 22 and a measurement is made of the temperature of the outer lining 22. A curve is drawn with one of the scales of the curve representing the outside or calibration temperature and the other scale representing the temperature of the outer lining 22. An unknown temperature on the outside of the temperature sensing unit il can be determined from the curve by adjusting the coolant ow rate to set the temperature of the inner lining 22 to the calibration value and the temperature of the outer lining 22 indicates the outside temperature on the calibration curve.

The following are exemplary dimensions and conditions for a temperature sensing unit like that shown in FIG. 6 for measuring an outside `temperature in the range of from 4,000 to 5,000 F.

Inner diameter of outer shell 0.564. Outer diameter of outer shell 1.000. Inner diameter of inner shell 0.500. Outer diameter of inner shell 0.5 60". Thickness of lead-zirconate tita- 0.002.

nate linings. Inlet coolant temperature Variable below 200 F. Coolant how rate Adjustable to inlet temp.

The various temperature sensing units described up to this point are all positioned completely within the high temperature environments. Reference should now be made to a diilerent application of the invention wherein the temperature sensing unit is mounted within an opening in the wall of the housing surrounding the high temperature environment. This is shown in FIG. 8 where the temperature responsive unit t5 is mounted in a relatively large circular wall opening 20 where the high temperature environment is to the left of the wall 20. The unit includes an open ended cylindrical housing 41 having the same approximate size and shape as the opening 20. A sealing gasket 43 is inserted between the housing 4I and the defining wall of the opening 20. The housing il is made of a very low thermally conductive material, such as Planiton asbestos, so as to minimize the conduction of heat into the side of the housing. It is important that practically all of the heat be directed into the housing il through the opening 45 at the inner end of the housing. The housing 41 has a cylindrical bore 47 therein in the outer section of which is located a cylina' drical slab or block of material lila of a material which is a good heat and electrical insulator, such as mullite, alumina and the like. The slab itin serves a similar purpose to the outer shell l@ previously described. Another slab 10b similar to slab ida is mounted in the inner section of the bore 47. The coeliicient of thermal conductivity of the slabs itin and ltib is preferably much higher than the housing lll so that heat iiows directly through the unit S" in a longitudinal direction.

A thin cylindrical disc 22a of temperature responsive material, which may be the titanate ceramic materials referred to previously, is sandwiched between the slabs lila and lill). The titanate disc 22a has conductive coatings on the opposite sides thereof which are connected to conductors 36a and 33a. The conductors extend along spaced points between the slab rib and the inner walls of the housing 4l and then through an opening at the outer end of the housing.

A cylindrical disc 22h of a material similar to disc 22a is secured in face-to-face contact with the outer face of the outer slab Mb, the disc 222: having conductive coatings on the opposite sides thereof to which are connected conductors 3d!) and 38h. A protective coating 39h protects the coated disc 22b.

A cavity l2 for circulating a coolant is provided at the outer end of the housing All by a cup-shaped end cap member Sil suitably secured to the outer end of the housing 41. The end cap has a pair of openings 52 and S4 which respectively receive inlet and outlet pipes 17 and 18 The conductor pairs 36u-38a and 36h-38h extending to the discs 22a and 2211 respectively extend around opposite sides of the pipes 17 and i3 to the temperature indicating devices (not shown in FIG. 8).

The operation of the embodiment of the invention just described is identical to that previously described in connection with the embodiment of FIG. 6.

It should be understood that numerous modifications may be made in the various forms of the invention described above without deviating from the broader aspects thereof.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. A device for measuring temperatures comprising: a first body of material having a surface to be placed in Contact with the high temperature to be measured and a surface which is isolated therefrom, a temperature sensitive element made of an electrical insulating material and which is thin relative to said body so that the temperature gradient thereacross is insigniiicant, said temperature sensitive element being in contact with the latter surface of said body, means for cooling the latter surface of said body to provide a temperature gradient across said surfaces, and means responsive to said temperature sensitive element for measuring the temperature of the adjacent surface of said body from which measurement the high temperature can be obtained in conjunction with other known quantities associated with said device.

2. A device for measuring temperatures comprising: a rst body of material having a surface to be placed in Contact with the high temperature to be measured and a surface which is isolated therefrom, a temperature sensitive element made of an electrical insulating material and Which is thin relative to said body so that the temperature gradient thereacross is insignificant, a second body made of a material having the same thermal conductivity as said first body, said temperatur sensitive element being sandwiched between said first and second bodies, means for feeding a coolant adjacent the surface of said second body remote from said first body to provide a temperature gradient across said bodies, and means responsive to said temperature sensitive element for indicating the temperature of the adjacent surfaces of said iirst and second bodies from which measurement the high temperature can be obtained in conjunction with other known quantities associated with said device.

3. A device for measuring temperatures comprising: a first body of material having a surface to be placed in contact with the high temperature to be measured and a surface which is isolated therefrom, a temperature sensitive element made of a ferroelectric material whose capacitance varies with temperature and which is thin relative to said body so that the temperature gradient thereacross is insignificant, said temperature sensitive element being in contact with the latter surface of said body, means for cooling the latter surface of said body to provide a temperature gradient across said surfaces, and to set the temperature of said temperature sensitive material below the Curie point temperature thereof, and means responsive to the capacitance of said temperature sensitive element for indicating the temperature of the adjacent surface of said body from which measurement the high temperature can be obtained in conjunction with other known quantities associated with said device.

4. A device for measuring temperatures comprising: a first body of material having a surface to be placed in contact with the high temperature to be measured and a surface which is isolated therefrom, a temperature sensitive element made of a erroelectric material whose capacitance varies with temperature and which is thin relative to said body so that the temperature gradient thereacross is insignificant, said temperature sensitive element being in contact with the latter surface of said body, means for cooling the latter surface of said body to provide a temperature gradient across said surfaces, and to set the temperature of said ferroelectric material below and in the region of the Curie point temperature thereof, and means responsive to the capacitance of said temperature sensitive element for indicating the temperature of the adjacent surface of said body from which measurement the high temperature can be obtained in conjunction with other known quantities associated with said device.

5. Apparatus for measuring temperature with a temperature responsive element which cannot operate at such high temperatures, said apparatus comprising: a body having a cavity therein, a thermally responsive ferroelectric material lining said cavity and having a pair of terminals across which a variation in an electrical characteristic appears with variation in temperature, means for cooling said cavity for providing a temperature gradient between the outside of said body and the surface of said cavity, and means for measuring the electrical characteristic of said tferroelectiic material.

6. Apparatus for measuring temperature with a temperature responsive element which cannot operate at such high temperatures, said apparatus comprising: a body having a cavity therein, a non-polarized ferroelectric material lining said cavity whose capacitance varies with temperature and having a pair of terminals across which a variation in capacitance appears with variation iri temperature, means for cooling said cavity for providing a temperature gradient between the outside of said body and the surface of said cavity, and for setting the ternperature of said ferroelectric material below its Curie point temperature and means for measuring the capacitance of said ferroelectric material.

7. Apparatus for measuring temperature with a temperature responsive element which cannot operate at such high temperatures, said apparatus comprising: a body of material having `an outer surface to be subjected to said temperature and an inner surface isolated therefrom, a non-polarized ferroelectric layer of material disposed in said body and having a pair of terminals across which the variation in an electrical characteristic thereof appears with variation in temperature, means for circulating a coolant along said inner body surface for providing a temperature gradient between the outside of said body and said surface, and means for measuring the electrical characteristic of said ferroelectric material.

8. Apparatus for measuring high temperature comprising: a thick-walled hollow body made of a material which is a relatively poor conductor of heat at the temperatures to which said body is to be subjected, means for circulating a coolant in said hollow body for providing a substantial temperature gradient across the outer and inner surfaces of said hollow body, 'and means for measuring the temperature inside said hollow body at a point where the temperature is substantially below the tempera-ture on the outside of said hollow body whereby the temperature on the outside of said body can be deter-mined from the measured temperature and other `known quantities associated with said apparatus.

9. In combination, a high temperature environment, and a device for measurement of the temperature of said environment comprising: an open-end housing made of a heat insulation material, a pair of slabs of heat insulating material of substantially the same coefficient of thermal conductivity within said housing, the open end of said housing being inserted in said source of high temperature such that only the outer surface of one of said pair of slabs is subjected directly to said high temperature environment, a rst temperature sensitive element sandwiched between said slabs and which is thin relative to said slabs, means for cooling the outer surface of the slab which is remote `from said high temperature environment to provide a temperature gradient through the slabs, and means responsive to said temperature sensitive element for measuring the temperative `of the surfaces of said slabs contiguous to the temperature sensitive element.

10. in combination, a high temperature environment, and a device for measurement of the temperature of said environment comprising: an open end housing made of a heat insulation material, a pair of slabs of heat insulating material of substantially the same coeflicient of thermal conductivity within said housing, said slabs having a much higher coefficient of thermal conductivity than said housing, the open end of said housing being inserted in said source of high temperature such that only the outer surface of one of said pair of slabs is subjected directly to said high temperature environment, a iirst temperature sensitive element sandwiched between said slabs and which is thin relative to said slabs, a second temperature sensitive element made of a heat insulation material which is thin relative to said slabs, the latter element being in contact with the outer surface of said slab remote `from said high temperature environment, means ifor cooling the latter surface to provide a temperature gradient through the slabs, and means responsive to said temperature sensitive elements for measuring the temperature of the surfaces of said slabs contiguous to the temperature sensitive element.

11. Apparatus for measuring high temperatures with a temperature responsive element which cannot operate at such high temperatures, said apparatus comprising: a thick-walled body made of a refractory material having poor heat and electrical conductivity relative to metal, said body having a cavity therein isolated from the portion of the body which is to be subjected to such high temperature, means for Afeeding a coolant into and out of said cavity rfor providing a substantial temperature drop between the outside of said hollow body and with the defining wall surface of said cavity, means for stabilizing the temperature of the coolant owing into the cavity, means for controlling the rate of flow of the cool- CII l0 ant circulating in said cavity, an electrical temperatureresponsive element in said body at a point where the temperature is substantially below the high temperature on the outside of said hollow body, and means responsive to said electrical temp rature-responsive element for indicating the temperature of said point within said hollow body, `whereby temperature on the outside of said hollow body can be determined `from other `known quantities and the measured temperature.

12. A device for measurement of temperature comprising a closed hollow body, a temperature sensitive element within said closed hollow body of substantially the same shape thereof and in contact with the inner surface thereof, means for feeding coolant into and out of the interior of said closed hollow body to provide a temperature gradient between the inside and outside of said hollow body, and means responsive to said temperature sensitive element for indicating the temperature in said body.

13. A device for measurement of high temperature comprising a iirst closed hollow body, a temperature sensitive element lining the inside of said iirst closed hollow body, a second hollow body located and being within said temperature sensitive element of the same material and substantially the same shape thereof and in contact with the inner surface thereof, means for feeding coolant into and out of the interior of said second hollow body, means for measuring the temperature within the interior of said second hollow body, and means responsive to said temperature sensitive element for indicating the temperature thereof.

14. A device as recited in claim 13 wherein said iirst and second hollow bodies are spherical in shape.

15. A method of measuring high temperatures comprising the steps of: passing a coolant through a hollow body to provide `a temperature gradient through the body walls, placing the hollow body in a calibration temperature environment, adjusting the temperature of the calibration environment to a number of predetermined temperatures and, while `maintaining the input coolant temperature at a given predetermined level, adjusting the flow rate of the coolant to maintain a iiXed temperature on the inside of said hollow body at the various calibration temperatures of said calibration environment, preparing a calibration curve with the calibration temperature and llow rate variables as the orthogonal scales for the curve, then placing the hollow body in an unknown temperature en vironment and, while maintaining the input coolant temperature at said predetermined temperature, adjusting the flow rate to provide a temperature on the inside of said hollow body equal to said predetermined temperature, and determining the unknown outside temperature from said calibration curve.

References Cited in the iile of this patent UNITED STATES PATENTS 430,271 Cooper June 17, 1890 2,027,405 Smede Jan. 14, 1936 2,054,382 Larsen et al Sept. 15, 1936 2,648,823 Kock et al. Aug. 11, 1953 3,018,663 Dunlop Jan. 30, 1962 

1. A DEVICE FOR MEASURING TEMPERATURES COMPRISING: A FIRST BODY OF MATERIAL HAVING A SURFACE TO BE PLACED IN CONTACT WITH THE HIGH TEMPERATURE TO BE MEASURED AND A SURFACE WHICH IS ISOLATED THEREFROM, A TEMPERATURE SENSITIVE ELEMENT MADE OF AN ELECTRICAL INSULATING MATERIAL AND WHICH IS THIN RELATIVE TO SAID BODY SO THAT THE TEMPERATURE GRADIENT THEREACROSS IS INSIGNIFICANT, SAID TEMPERATURE SENSITIVE ELEMENT BEING IN CONTACT WITH THE LATTER SURFACE OF SAID BODY, MEANS FOR COOLING THE LATTER SURFACE OF SAID BODY TO PROVIDE A TEMPERATURE GRADIENT ACROSS SAID SURFACES, AND MEANS RESPONSIVE TO SAID TEMPERATURE SENSITIVE ELEMENT FOR MEASURING THE TEMPERATURE OF THE ADJACENT SURFACE OF SAID BODY FROM WHICH MEASUREMENT THE HIGH TEMPERATURE CAN BE OBTAINED IN CONJUNCTION WITH OTHER KNOWN QUANTITIES ASSOCIATED WITH SAID DEVICE. 